This longitudinal, case-control pilot study examined amygdala growth in rhesus macaque infants receiving the complete US childhood vaccine schedule (1994-1999). Longitudinal structural and functional neuroimaging was undertaken to examine central effects of the vaccine regimen on the developing brain. Vaccine-exposed and saline-injected control infants underwent MRI and PET imaging at approximately 4 and 6 months of age, representing two specific timeframes within the vaccination schedule. Volumetric analyses showed that exposed animals did not undergo the maturational changes over time in amygdala volume that was observed in unexposed animals. After controlling for left amygdala volume, the binding of the opioid antagonist [11C]diprenorphine (DPN) in exposed animals remained relatively constant over time, compared with unexposed animals, in which a significant decrease in [11C]DPN binding occurred. These results suggest that maturational changes in amygdala volume and the binding capacity of [11C]DPN in the amygdala was significantly altered in infant macaques receiving the vaccine schedule. The macaque infant is a relevant animal model in which to investigate specific environmental exposures and structural/functional neuroimaging during neurodevelopment.

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Basically, they took 16 monkeys (rhesus macaque or Macaca mulatta). 12 of them were given vaccines in a schedule intended to mimic the U.S. vaccine schedule of the 1990’s, including thimerosal (which was added). 4 were given saline injections (controls). MRI scans were taken. “Time One (T1) at approximately 4 months of age and Time Two (T2) at approximately 6 months of age.”

From the abstract we see that they found that the “Volumetric analyses showed that exposed animals did not undergo the maturational changes over time in amygdala volume that was observed in unexposed animals.”

In other words, the amygdala volume was different from the controls at T2 for the monkeys given vaccines.

Want some more detail? Well, in regards to the right amygdala:

For the exposed group there was a nonstatistically significant increase in right amygdala volume over time (P=0.16; Table IIa). For the unexposed group there was a significant drop in right amygdala volume over time (P

Read that again. Did they just say that a piece of the brains of the control animals shrank between 4 months of age and 6 months of age?

They did. That’s what their data show. It seemed so odd to me that I double (and triple) checked. I’m sort of visual in how I like to take in data, so here is Figure 4(A) from the paper. This shows the left amygdala size for the two times (T1=4 months of age and T2=6 months of age). I’ve added text to the graph. It is in red so you know what I added. (click to enlarge)

The dotted lines are for the “exposed” animals. I.e. those vaccinated. The solid line is for the “unexposed” animals. See how at T1 they have amygdala sizes that are about the same size? But at T2 (2 months later) the amygdalas of the “unexposed” animals have shrunk, while the amygdalas of the exposed/vaccinated animals grew a little.

I’m not a primate expert, but it bothers me somewhat to hear that a piece of the brain might shrink. I would expect in my own naive way that pieces of the brain would grow as monkeys mature, so I decided to check: has anyone looked at amygdala size in Rhesus Macaques as a function of age? It turns out there is a paper just out in 2009, “Maturation of the Hippocampal Formation and Amygdala in Macaca mulatta: A Volumetric Magnetic Resonance Imaging Study” by Christa Payne et al. from the University of Texas and Emory University. They also were working with small numbers (11 in the male group). Here is Figure 6(A) from that paper:

One line is for the left amygdala, and one for the right. Same with the datapoints, the filled are for one side, the hollow for the right. But the basic idea is clear—the amygdala grows with time in monkeys, not shrink. Yes, seems obvious, but I had to check.

How could the Hewitson paper report that the control monkeys have shrinking amygdalas? One possible answer: too few monkeys in the control group. There is a lot of scatter in the amygdala data from the U. Texas paper. If someone has only a couple of datapoints, they might get some strange results.

The Hewitson paper had really small numbers:

“A complete set of MRI data at both T1 and T2 were obtained from 9 exposed and 2 unexposed animals.”

But, wait, remember above? Weren’t there 4 monkeys in the control group and 12 monkeys in the vaccinated group? What happened to the other 2 of the control subjects? There weren’t many to begin with but half of the control group are missing in the data? What’s the reason for that? No, that’s a real question which I can’t find answered in the paper: what happened to the two other controls?

This paper is generating quite a bit of interest in places like the Age of Autism blog. Unfortunately for them, this paper is not the genie getting out of the bottle. Just another low quality paper. Just another 16 monkeys giving their lives for nothing.

1 comment(s) for this post:

Sullivan:2010-Jul-16 It is very hard to not get snarky on this one, but this is one bad study. I'm stunned it got published. There is a reason why it isn't in a first-line (or second line) journal. They have 2 control animals. Two. They had 4 but they just don't report on half of them?!? The amygdalas are shrinking in their control animals with time?!? What a waste of time, money and primates.